WBR0251
| Author | [[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D. and Alison Leibowitz [1])]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Microbiology |
| Sub Category | SubCategory::Infectious Disease |
| Prompt | [[Prompt::A 34-year-old woman presents to the physician’s office with complaints of fever and abdominal pain. The patient states that she is currently in day-10 of her menstrual period, but she noted vaginal spotting earlier this morning. She is sexually active and applies an intrauterine device for contraception. She denies smoking, alcohol intake, and any known drug allergies. Her temperature is 38.7 °C (101.7 °F), blood pressure is 128/86 mmHg, and heart rate is 98/min. Physical examination is remarkable for suprapubic tenderness upon light palpation. Pelvic exam shows local vaginal swelling with suppurative discharge. Immunofluorescence with direct smears reveals a non-acid-fast, gram-positive rods with branching filaments. The physician prescribes an oral pharmacological agent to treat the patient's condition. What is the mechanism of action of the prescribed pharmacological agent?]] |
| Answer A | AnswerA::Blocks transpeptidase cross-linking |
| Answer A Explanation | AnswerAExp::Oral penicillin is the first line agent to treat uncomplicated cases of pelvic actinomycosis. Penicillin blocks transpeptidase cross-linking of peptidoglycan. |
| Answer B | AnswerB::Binds D-ala D-ala to inhibit cell wall peptidoglycan formation |
| Answer B Explanation | AnswerBExp::Vancomycin binds D-ala D-ala to inhibit cell wall peptidoglycan formation. |
| Answer C | AnswerC::Inhibits formation of the initiation complex |
| Answer C Explanation | AnswerCExp::Aminoglycosides inhibit the formation of the initiation complex and cause mRNA misreading. |
| Answer D | AnswerD::Binds to 30S and prevents attachment of aminoacyl-tRNA |
| Answer D Explanation | [[AnswerDExp::Tetracyclines bind to 30S and prevents attachment of aminoacyl-tRNA. Tetracyclines, along with clindamycin and erythromycin, may be administered to treat actinomycosis, but they are reserved for patients with penicillin allergy. However, the patient in this vignette may be prescribed penicillin since she denies known drug allergies.]] |
| Answer E | AnswerE::Binds to 23S of the 50S ribosomal subunit and block translocation |
| Answer E Explanation | [[AnswerEExp::Macrolides bind to 23S of the 50S ribosomal subunit and block translocation. Erythromycin, along with clindamycin and tetracyclines, may be administered to treat actinomycosis, but they are reserved for patients with penicillin allergy. However, the patient in this vignette may be prescribed penicillin since she denies known drug allergies.]] |
| Right Answer | RightAnswer::A |
| Explanation | [[Explanation::Pelvic actinomycosis is a rare infection that is strongly associated with long-lasting application of contraceptive intrauterine device or use of vaginal pessary. The infection results in local swelling with abscess formation and suppurative discharge. If left untreated, it may lead to tissue fibrosis and fistulisation. Pelvic actinomycosis may manifest as fever, suprapubic pain, and inter-menstrual bleeding. Actinomycosis is caused by Actinomyces israelii, a non-spore, non-acid-fast, anaerobic, gram-positive rod that forms long branching filaments resembling fungi. Actinomyces israelii is part of the normal flora of the oropharynx, GI tract, and the female genital tract. Characteristically, Actinomyces invades tissues in a neoplasm-like pattern with contiguous spread, making malignancies among the list of differential diagnosis of the disease.
The organism is difficult to grow with routine culture techniques since it is oxygen-sensitive and grows relatively slowly, which might delay the diagnosis until definitive culture results return after 2 to 3 weeks. Nonetheless, immunofluorescence with direct smears may provide a fast diagnosis, revealing gram-positive rods with branching filaments along with identification of sulfur granules on methylene blue stain. Management is by administration of oral penicillin in uncomplicated cases (clindamycin, erythromycin, or tetracycline may be administered to patients with penicillin allergy), surgical drainage of abscesses, and NSAIDs for symptomatic relief. Penicillin blocks transpeptidase cross-linking of peptidoglycan and activate autolytic enzymes. They are also administered in infections due to other gram-positive organisms (such as S. pneumoniae and S. pyogenes), some gram-negative organisms (such as N. meningitidis), and spirochetes (T. pallidum that causes syphilis). |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Pelvic actinomycosis, WBRKeyword::Penicillin, WBRKeyword::Mechanism of action, WBRKeyword::Antibiotics, WBRKeyword::Actinomyces israelii, WBRKeyword::Actinomyces, WBRKeyword::Vaginal discharge, WBRKeyword::Suprapubic pain, WBRKeyword::Abdominal pain, WBRKeyword::Intrauterine device, WBRKeyword::IUD, WBRKeyword::Pessary, WBRKeyword::Sulfur granules, WBRKeyword::Branching filaments, WBRKeyword::Gram-positive, WBRKeyword::Rod |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |